1. Field of the Invention
This invention relates to a method and apparatus for displaying upon a viewing surface an image simulating a plane surface area illuminated by a light source, and more particularly to an image simulating the ground area illuminated by a light source as viewed from an eyepoint within an aircraft.
2. Description of the Prior Art
Use of an aircraft simulator is a modern well known method of training aircraft personnel. In a simulator the trainee is placed in a realistically recreated aircraft environment designed such that the trainee feels he is in and operating an actual aircraft without leaving the ground.
An important element that is used to create this realism is the visual display system. Many training judgments depend on the student's response to a visual cue. During flight operation a pilot views his external environment through his aircraft window. For instance, while taking off and landing he scans the runway and operates his controls to properly maneuver his aircraft.
Many modern simulators utilize the viewing surface of a raster-scanned television display to simulate a window view. The external environment seen by the pilot as he looks out the window is produced as the beam of the television cathode ray tube traces the raster across the viewing surface.
The input image to the television display can be generated in a number of different well known ways. Prior art camera model image generation systems use a TV camera and an optical probe which are positioned over a scale model of a simulated terrain. The probe views the model board and the TV camera records the image which is then processed and displayed on the CRT. The accuracy of the display created depends to a large extent on the accuracy of the model board viewed.
Prior art Synthetic Terrain Generators (STG) create an artificial scene on the television display by electronic means. Current STG methods, as described in U.S. Pat. Nos. 3,911,597 and 4,054,917, utilize a fixed pattern of intersecting grid lines on a ground plane. This intersecting pattern of grid lines is by its very nature a synthetic representation of an actual ground surface and is not an accurate real life situation as would be seen by one looking through an aircraft window.
Most aircraft employ landing lights and spot lights. They are typically located at some point distant from the pilot, on the wings or the belly of the aircraft, for example. The source of the directed beam of light produced by these lights can be either fixed to the body of the aircraft or rotatable relative to the body of the aircraft. These lights aid the pilot during night operation by providing ground illumination. Both geographical references and altitude cues are provided. Landmarks become more clearly defined during runway approaches. Some aircraft, helicopters in particular, find search lights extremely important where landing and taking off from confined landing areas are required.
Prior art simulators impose a burden on trainees learning night operations by not providing an accurate simulation of an illuminated ground area.
In the prior art camera model system this ground illumination was simulated by attaching a light to the probe. This rigidly mounted light is not servo-controlled and thereby does not properly respond to a simulated aircraft's pitch, roll, and altitude changes. Also, since the scale factor of the model board is typically 1,000:1, the placement of the attached light cannot be made to correspond to the actual displacement between an aircraft mounted light and the simulated eyepoint, since the physical dimensions of the probe are too large for properly scaled placement.
Furthermore, a unique characteristic produced by the directed beam of light, namely the change in shape of the illuminated ground area during changes in aircraft attitude and position, is not provided. A directed beam of light from a light source, as would be the case with landing lights or search lights, is typically represented as a cone of light. As an aircraft changes its attitude and position the ground area illuminated by this cone of light will change its shape since the cone of light will be seen to be intersecting the ground from a new direction. The probe-mounted light does not allow for these illuminated area changes.
Prior art synthetic terrain generators, as previously mentioned, only provide a synthetic display of a fixed pattern of intersecting grid lines. Changes in this fixed pattern of grid lines can occur with changes in the aircraft's attitude and position relative to the grid pattern. However, no provision is found in the STG's whereby a changeable illuminated ground area generated by a fixed or rotatable source of light can be produced. Existing STG's do not simulate terrain illumination.
With aircraft and other type simulators being extensively used as training devices, a need arises for simulation systems that have a high degree of realism. Proper training requires accurate visual systems. It therefore becomes particularly necessary in those simulators which are recreating directed beams of light illuminating a plane surface that a visual system be provided which has an accurate simulation of this significant visual cue.